Abstract
Nanocomposite–parylene C (NCPC) thin films were deposited with a new technique based on the combination of chemical vapor deposition (CVD) for parylene C deposition and RF-magnetron sputtering for silver deposition. This method yields good dispersion of Ag-containing nanoparticles inside the parylene C polymer matrix. Film composition and structure were studied by using several techniques. It was found that the plasma generated by the RF-magnetron reactor modifies the film density as well as the degree of crystallinity and the size of parylene C crystallites. Moreover, silver is incorporated in the parylene matrix as an oxide phase. The average size of the Ag oxide nanoparticles is lower than 20 nm and influences the roughness of the NCPC films. Samples with various contents and sizes of silver-oxide nanoparticles were investigated by broadband dielectric spectroscopy (BDS) in view of their final application. It was found that both the content and the size of the nanoparticles influence the value of the dielectric constant and the frequency-dependence of the permittivity. In particular, β-relaxation is affected by the addition of nanoparticles as well as the dissipation factor, which is even improved. A dielectric constant of 5 ± 1 with a dissipation factor of less than 0.045 in the range from 0.1 Hz to 1 MHz is obtained for a 2.7 µm thick NCPC with 3.8% Ag content. This study provides guidance for future NCPC materials for insulating gates in organic field-effect transistors (OFETs) and advanced electronic applications.
Highlights
Increasing the dielectric constant of gate dielectrics for oxide thin-film transistors (TFTs) improves the performance of such devices
Parylene C is a well-controlled material when used as gate dielectric, which is a crucial requirement for the performance of the organic field-effect transistors (OFETs) and for the device reliability
Nanocomposite–parylene C (NCPC) were synthetized at room temperature by chemical vapor deposition polymerization of parylene C combined with RF-sputtering of silver
Summary
Increasing the dielectric constant of gate dielectrics for oxide thin-film transistors (TFTs) improves the performance of such devices. Using a sol–gel approach, high-k ink hybrid AlOOH nanocomposites demonstrated low leakage currents suitable for low operating voltages of TFTs [2] These approaches can not be used when parylene C (PPXC) is chosen as gate dielectric as the only proven process for producing high-quality PPXC layers is chemical vapor deposition (CVD). Its deposition process makes it accessible as a coating for many semiconductor polymers [10] for organic field-effect transistors (OFETs) [11], organic light-emitting diodes (OLEDs) [12,13], and flexible organic electronic devices (FEDs) [14,15]. Hydrophobicity [26] and physical stability [27] of parylene C make it a good candidate as a coating dielectric material to protect the sensitive organic layer from oxygen and water vapor [28], which are among the greatest degradation mechanisms contributing to the electrical instability of OFETs [29,30,31,32] and oxide TFTs [33]
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